1. Field of the Invention
This invention relates generally to the fields of molecular biology and molecular medicine and more specifically to the identification of proteins involved in innate immunity, programmed cell death, NFKB induction, cytokine processing and inflammation, and associations of these proteins.
2. Background Information
Proteins containing the death domain fold (DDF) play pivotal roles in programmed cell death (apoptosis) and inflammatory responses. The DDF represents a protein interaction motif consisting of a bundle of (usually) six antiparallel α-helices. This core structure is found in at least three families of evolutionarily conserved and closely related domain families, including Death Domain (DD), Death Effector Domain (DED) and Caspase Recruitment Domain (CARD) families.
CARD- and DED-family proteins have been implicated in activation of Caspase-family proteases. Though many of these intracellular cysteine proteases are involved in apoptosis induction, some of these proteases, such as Caspase-1, are chiefly responsible for proteolytic processing and activation of pro-inflammatory cytokines, such as Interleukin-1β. Homotypic interactions among CARD- and DED-containing adapter proteins occur with the inactive proforms of those Caspases which possess N-terminal prodomains containing complementary CARDs or DEDs, respectively. The resulting formation of multi-protein complexes leads to protease cleavage and activation by an induced proximity mechanism in which pro-proteases are clustered together, permitting trans-proteolytic cleavage events necessary for generation of active Caspases.
Besides regulating Caspase activation, some DDF proteins are also known to participate in activation of transcription factor NF-KB, a family of dimeric transcription factors containing the Rel-homology domain (RHD). In mammals, NF-KB family members play critical roles in regulating expression of genes involved in inflammatory and immune responses, including certain cytokines, lymphokines, immunoglobulins, and leukocyte adhesion proteins. Among the DDF proteins, DD- and CARD-containing proteins have been shown to participate in NF-KB induction, with certain DD-family proteins linking cytokine receptors to downstream adapter proteins implicated in IKK activation and specific CARD-family proteins linking to adapter proteins that connect to the IKK complex.
The identification of proteins with folds that structurally resemble the Death Domain Fold, determination of molecules with which they interact, and elucidation of their biological function, can form the basis for strategies designed to alter apoptosis, NFKB inductions, immune and inflammatory responses, cytokine production, and other cellular processes mediated by these proteins. Thus, a need exists to identify proteins with structural resemblance to DDF proteins, and to identify functional domains within these proteins. The present invention satisfies this need and provides additional advantages as well.